Patients will be stratified on the basis of age/Tanner stage and ability to swallow intact capsules. Patients will be randomized to either Balanced Dose or Low Dose RTV treatment arms. Patients in the Balanced Dose Arm will receive RTV and IDV in approximately equal doses. The Low Dose RTV Arm will receive a dosing ratio of RTV:IDV of approximately 1:3. Patients will have scheduled study visits every 4 weeks for 6 months, then every 3 months for approximately 18 months. Study visits will consist of a medical history, physical exam, and blood and urine tests. Patients will have intensive pharmacokinetic analysis at Week 4 (or 2 weeks after a stable dose of study drugs has been reached) and Week 16. Study visits that include pharmacokinetic analysis will last 9 to 13 hours.